Within the framework of the present embodiment, “parameters related to a flight of an aircraft” is intended to mean flight parameters of the aircraft, such as an air speed, an incidence or a Mach number of the aircraft, and parameters outside the aircraft and encountered by the aircraft in the course of the flight, such as the total temperature for example.
Such parameters related to a flight of an aircraft are generally determined with the aid of measurements carried out on the aircraft on the basis of probes, such as total pressure, total temperature or incidence probes. However, meteorological phenomena, such as ice in particular, can have effects on sensors and probes which may even lead to an impairment of the measurement carried out, rendering it sometimes erroneous (fixed or biased). The object of the present embodiment is in particular to remedy this drawback.
It is known that an aircraft, especially a transport airplane, is generally provided with an anemobarometric platform of ADC (“Air Data Computer”) type which provides, in real time, a conventional speed of CAS (for “Calibrated Air Speed”) type. Accordingly, this anemobarometric platform is associated with total pressure probes (Pitot tubes), and it may, for example, form part of an air data and inertial data system of ADIRS (for “Air Data Inertial Reference System”) type, which represents a platform of inertial references integrating the functions of the anemobarometric platform. However, erroneous or absent air data (air speeds in particular) may, for example, appear during system faults, erroneous information from sensors, or in the presence of icing or ice crystals.
Patent FR-2 979 993 describes a method and device making it possible to provide an alternative air speed, able to be determined even in case of failure of an anemobarometric platform and/or pressure probes associated therewith, in particular Pitot probes. Accordingly, this patent FR-2 979 993 discloses in particular a method for automatically estimating a particularly accurate air speed of an aircraft that can be determined even in the presence of erroneous air data. This method makes provision, for this purpose, to compute an air speed termed the aerodynamic speed, on the basis of the current values of parameters (mass, load factor, incidence, etc.) related to the aircraft and comprising aerodynamic parameters, to receive a current conventional speed, generated by an anemobarometric platform, to subtract an estimated speed from this conventional speed so as to obtain a residual speed, to compare this residual speed with a threshold value, and as a function of this comparison as long as the residual speed is less than or equal to the threshold value, to integrate it so as to obtain a corrective value which is added to the aerodynamic speed so as finally to obtain the estimated air speed; and as soon as the residual speed is greater than the threshold value (for a duration of confirmation), illustrating the detection of a problem of validity of the conventional speed, and as long as this remains the case, to add a fixed corrective value to the aerodynamic speed to obtain the estimated air speed.
This method for automatically estimating the air speed of the aircraft makes it possible to obtain a good estimation of the air speed, in case of temporary failure of the total pressure probes.
This method for automatically estimating the air speed uses in particular a value of the angle of incidence of the aircraft to compute the air speed. The angle of incidence (or “angle of attack”) is the angle between a reference line on the aircraft and the direction of movement of the aircraft with respect to the air mass which surrounds it. This angle is generally provided in real time by incidence probes, formed by wind vanes mounted on the outside surface of the aircraft.
However, in certain particular cases, ice may form at the level of the incidence probes and disturb their operation, thereby preventing a reliable indication of the angle of incidence from being available on the aircraft. Furthermore, if a disturbance of the operation of the total pressure tubes occurs simultaneously with such a disturbance of the operation of the incidence probes, the aforementioned method of automatically estimating the air speed cannot proceed correctly.